Electric cable



Patented Jan. 2, 1934 UNITED STATES PATENT OFFICE ELECTRIC CABLE ThomasNixon Riley, London, England, assignor to International StandardElectric Corporation, New York, N. Y.

No Drawing. Application August 29, 1930, Serial No. 478,775, and inGreat Britain March 5,

3 Claims. (01. 91-70) This invention relates to the manufacture ofelectric cables and particularly to cables having impregnated fibrousdielectrics. i

In manufacturing cables of the impregnated 5 dielectric typedifiiculties have been experienced in the cable-during itsmanufactureone or more substances, or a pre-impregnating medium, which during orafter the final drying operations can be evaporated to assist inexpelling the air or residual air from the dielectric. The substance ormedium may be applied to the core or to a convenient part of theinsulation et the cable and is-preferably such that it will not beevaporated during the initial stages of the drying of the dielectric.The medium employed should be one which is not harmful to the electricproperties of the insulation and preferably one which is beneficialthereto or to the manufacture of the cable generally. The medium shouldalso be such that it will condense to a liquid or solid form attemperatures normallyexperienced duringthe 7 working of the cable. Insome instances, the

medium may be mifed with another or other substances adapted toaccelerate or retard its evaporation or if it be a liquid to bring it tosolid form for application.

In ca y g the invention into efiect according to one convenient mode asapplied to the manufacture of high voltage cables, the copper core afterstranding may be passed through a bath of, or otherwise treated orcoated with a vaporizable material which is such that it does notevaporate up to temperatures of the order of 100 C. at ordinaryatmospheric pressure and then the insulation applied to the 'core in theordinary manner. Alternatively, the whole or a part of the fibrousinsulation may be impregnated with the vaporizable material before orafter it is applied to the cable and thereafter varnished with asuitable retaining medium which may be of a resinous nature. An exampleof a suitable vaporizable material is methyl naphthalene, but it is tobe understood that various other substances may be employed. At theappropriate time the cable is placed in an impregnating vessel which maybe a tank or the outer sheath of the cable, this container is thenevacuated so that the greater part of the air is removed from thedielectric of the cable.

During the initial stages of the drying Of the dielectric thetemperature and the pressure are maintained at such values that thepre-impregnating medium is not vaporized to any considerable extent.Towards the end of the drying operations or after they have beencompleted the temperature is raised, as for example, by passing anelectric current through the core, to such an extent that thepre-impregnating medium is vaporized and gradually replaces the residualair in the body of dielectric material.

After further vacuum treatment if desired the impregnating compound maybe admitted to the containing vessel inthe usual manner. If desired,acondenser may be provided and arranged in the vacuum system so that thevaporizable material which is evaporated from the cable can berecovered.

It will be appreciated from the foregoing that the invention not onlyprovides a convenient way of expelling or assisting in the expelling ofair from the cable but also provides a convenient method whereby varioussubstances may be introduced into, or incorporated in the dielectric ofthe cable. This may be taken advantage of for rendering the cable moreamenable to subsequent treatment or impregnation, for instance byimproving the absorption properties of the dielectric, or for otherpurposes.

What is claimed is:

1. A method of impregnating an electric cable comprising applying avaporizable material to the conductive core, surrounding said core withinsulation, subjecting the insulated core to a drying operation under apredetermined diminished pressure and at a predetermined temperature,

raising the temperature and decreasing the pressure and then introducingan impregnating medium into said cable.

2. An electric cable in the process of manufacture having a conductivecore surrounded by insulation and methyl naphthalene associatedtherewith.

3. A step in the process of manufacturing electric cables whichconsistsin associating methyl naphthalene with the cable prior to the dryingoperation. I

THOMAS NIXON RILEY.

